Comparison of true-height electron density profiles derived by POLAN and NHPC methods

The changing state of the ionosphere is generally monitored by networks of vertical ionosondes that provide us with regular ionospheric sounding. Many ionospheric applications require determination of the true-height electron density profiles. Therefore, ionograms must be further inverted into real-height electron density profiles. The paper presents the comparison study of the true-height electron density profiles inverted from ionograms using two different methods POLAN (Titheridge, 1985) and NHPC (Huang and Reinish, 1996; Reinish et al., 2005), widely used by the ionospheric research community. Our results show significant systematic differences between electron density profiles calculated by these two inversion methods. pkn@ufa.cas.cz     

Prediction of tunnel lining loads using correction factors

A design method for the prediction of lining loads should include the decrease of lining loads due to the stress release before lining installation and the increase of lining loads due to development of ground yielding. Schwartz and Einstein included both factors in their original closed form solutions in the form of a support delay factor λ_d and a yield factor λ_y respectively. The validity of the design method is reviewed by comparing the loads calculated using the methods with the field measurements obtained from several tunnels. The possible causes of the load discrepancy between measurements and predictions are presented.

Schwartz and Einstein's proposed method gives reasonable results for tunnels with short delay lengths. However, the method could not be used reliably for tunnels either with long delay lengths or with voids between the soil and TBM due to the difficulties finding the pre-support ground movements and therefore λ_d.     

Comparison of the measured and modelled electron densities and temperatures in the ionosphere and plasmasphere during 20/30 January, 1993

We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earths ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20/30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(v) and O₂(v) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N₂ and O₂ and the second level of O₂, and the calculated distributions of N₂(v) and O₂(v) are highly non-Boltzmann at vibrational levels v > 2. The resulting effect of N₂(v > 0) and O₂(v > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N₂(v > 0) and O₂(v > 0), and inclusion of vibrationally excited N₂ and O₂ brings the model and data into better agreement.     

相空间重构中时滞判定的功率谱分析法

从再现系统原始信息和确定混沌关键指标角度,论证了相空间重构中时滞判定的重要性。构建基于时滞的时间序列自相关系数和自相关函数式,提出了时滞判定的功率谱方法。通过实际应用效果的比较,时滞判定的功率谱方法具有数据处理量较小和判别过程较稳定的优点,在一定程度上解决了Wolf方法确定Lyapunov指数鲁棒性较差的问题。     

Numerical Estimate of the Spectral Resonance Structure Frequency Scale of Natural ULF Magnetic Field

The spectral resonance structure (SRS) of the magnetic component of natural electromagnetic noise in the frequency range 0.5 – 2.5 Hz is investigated to estimate the frequency scale of the structure. The magnetic field data recorded at 49°20'N, 22°40'E, in the Bieszczady Mountains, Poland, at night hours of May 1996 – 2001 are used. It is assumed that the resonant frequency pattern of the ionospheric Alfvén resonance (IAR) appears in the spectral resonance structure. Both a model of the ionospheric Alfvén resonance for night-time conditions of the ionosphere and an algorithm of evaluating the frequency scale are presented. The algorithm is applied to the experimental data. The results are compared to those obtained with the International Reference Ionosphere model.     

An aquifer model with a parameter characterizing the inhomogeneity of media

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The climate attractor

Time series of proxy data representing long-term variation of the terrestrial climate presumably show aperiodic changes, which has given rise to the hypothesis that the dynamics of the earth’s climate is governed by a strange attractor. Here a study of such attractors is presented, with emphasis on determination of its dimension and the reported results. Finally, a one dimensional delayed albedo feedback climate model is discussed with the related strange attractor and its dimension.     

2018-08-25~29期间全球电离层TEC对地磁暴的响应分析

使用IGS提供的全球电离层地图对2018-08-26地磁暴期间TEC变化进行分析,利用滑动四分位距法提取全球TEC扰动特征,并初步探讨此次磁暴引起的电离层扰动响应机制。结果表明：1）磁暴主相期间,除北极地区外电离层TEC主要表现为正相扰动;在恢复相期间,电离层TEC在北半球呈现长期负扰,而在南半球则相反。2）磁暴期间全球电离层TEC扰动与热层成分O/N₂变化有关。星际磁场南向期间,东向快速穿透电场对全球日间电离层TEC正扰具有很大影响,高能粒子的沉降作用可能是高纬和极区TEC发生正扰的原因;夏冬季节环流会促进电离层在磁暴恢复相阶段的南北不对称响应。     

在大气折射延迟模型中避免采用大气分布模型的论证

天文大气折射是经典天体测量学和大地测量的一项误差源,大气折射延迟是空间大地测量技术中的一项重要误差源,它们的改正模型都直接与大气折射率和大气分布模型有关。文章简述了大气的垂直分布状况,以及大气折射率(或折射率差)因地和因方位而异的情况,分析了目前只能采用球对称大气分布模型的原因。论证了随测站和随方位而异的天文大气折射和电磁波大气折射延迟实测模型建立的必要性和可能性。实测模型已经包含了测站上空大气实际分布及其非球对称的特性,不必再去寻找或建立随地势而异和随季节而变的大气分布模型,避免了大气分布模型选择不当的影响,从而排除了空间大地测量技术中的一项主要误差源。     

中性大气对非差伪距定位的影响及其模型改正分析

中性大气包括对流层和平流层,它们对GPS信号造成的延迟影响是GPS定位的一个主要误差源。与电离层的影响相比,消除中性大气的延迟影响更复杂,只能用经验模型进行改正。本文就中性大气对GPS定位的影响进行详细地分析和说明,对中性大气改正模型及其相关问题进行明确地论述。最后以中国IGS跟踪站一年中不同季节的观测数据为基础,通过对相同的数据采用不同的中性大气改正模型分别进行相同的定位解算,并对不同模型的定位结果进行分析,得出有关中性大气模型改正与GPS定位之间及改正模型间的定性和定量的关系。